The present invention relates to a method for dyeing hair that has been subjected to a chemical reduction step, more particularly, to a method for dyeing such hair by means of at least one oxidoreductase and at least one chemical oxidizing agent such as peroxide.
Hair setting processes, including both permanent waving and straightening, are usually carried out at room temperature. The process typically includes at least two fundamental steps: i) reducing covalent disulfide linkages in the keratinous fibres of the hair, thereby rendering the hair deformable without elasticity, the hair typically being wetted by a solution containing a reducing agent and either rolled on curlers or mechanically straightened, and ii) rinsing and neutralization of the reducing agent, followed by re-establishment of a network of cross links in the keratinous fibres of the hair, either by air oxidation or by application of a so-called fixer (which usually contains an oxidizing agent), thereby rendering the curly or straightened shape xe2x80x9cpermanentxe2x80x9d.
For the purpose of breaking the disulfide cross links, a number of reducing agents can be used, including strong bases such as sodium hydroxide and guanidinium hydroxide, as well as weaker bases such as thioglycolic acid, thioacetic acid, and other mercamtans. Permanent waving processes typically use substances based on thioglycolate, whereas permanent hair straighteners (also known as xe2x80x9crelaxersxe2x80x9d) normally require more aggressive reducing chemicals, e.g., hydroxides, in order to achieve xe2x80x9cpermanentxe2x80x9d, straightening.
Among reagents used for the purpose of fixation of hair, i.e., compounds capable of re-establishing the physicomechanical properties of the hair by forming disulfide and other cross links between keratin chains, hydrogen peroxide (H2O2) is the most commonly used reagent as H2O2 reacts rapidly with the keratin xe2x80x94SH groups. Other examples of commonly used oxidizing agents are perborates, bromates, chlorites, iodates, bromates, persulphates and tetrathionates. These oxidative agents often over-oxidize and damage the hair, producing sulphonic acids such as cysteic acid instead of simply reforming disulfide bridges.
Hydrogen peroxide is also the conventional catalyst in is hair dyeing formulas, and it is important to recognize that peroxide concentrations used for hair dyeing formulas are significantly larger than those used to reform hair cross links in the oxidative, restorative phase of a hair setting treatment (also used at different pH).
It is possible, and not uncommon in home straightening treatments, to use atmospheric oxygen as an oxidizing agent for reformation of hair cross links. The direct use of atmospheric oxygen, however, suffers from the disadvantage that several hours are required in order to complete the reaction. This option is even less appealing when used in conjunction with permanent waving treatments, since hair fixation should occur while the hair is in the desired conformation; i.e., while the hair is on curlers.
Many consumers would like to apply a permanent dye at the same time as a permanent hair straightening (or waving) treatment. Unfortunately, this combination causes severe damage to the hair, primarily because the damage caused by exposure to high levels of H2O2 (i.e., more than 1% H2O2, such as those used in conventional hair dyes) is exacerbated when hair is in a damaged and vulnerable state as a result of exposure to strong reducing agents. For this reason, consumers are advised to wait at least two weeks between permanent straightening and permanent dyeing of hair. While temporary hair dyes can be applied to hair directly after a straightening treatment, there is a long-standing need and desire for a product that allows simultaneous permanent straightening and permanent dyeing of hair without excessive hair damage.
Permanent hair dyes are durable to sunlight, shampooing, and other hair treatments and are ordinarily refreshed periodically (about once a month) as new hair grows out. With these dyeing systems, the dyes are created directly in and on the hair. Small aromatic colourless dye precursors (e.g., p-phenylenediamine and o-aminophenol) penetrate deep into the hair where the precursors are oxidized by an oxidizing agent into colored polymeric compounds. These colored compounds are larger than the dye precursors and are not easily washed out of the hair.
Traditionally, H2O2 is used in concentrations of about 1-10%, normally from about 3-6%, as the oxidizing agent. The use of H2O2 in dye compositions has some disadvantages as H2O2 damages the hair. Further, conditions frequently used for oxidative dyeing require treatment at high pH (normally around pH 9-10), which also causes damage to the hair.
To overcome the disadvantages of using H2O2, it has been suggested to use oxidation enzymes to replace H2O2.
U.S. Pat. No. 3,251,742 (Revlon) describes a method for dyeing human hair by dye formation in situ (i.e., on the hair).
An oxidative enzyme is used for the colour formation reactions at a substantially neutral pH (pH 7-8.5). Laccases, tyrosinases, polyphenolases and catacolases are mentioned as suitable oxidation enzymes.
EP patent No. 504.005 (Perma S. A.) concerns compositions for hair dyeing which do not require the presence of H2O2 (hydrogen peroxide). The compositions comprise an enzyme capable of catalysing the formation of the polymeric dyes and also dye precursors, such as bases and couplers, in a buffer solution wherein the pH of the composition is between 6.5 and 8 and the enzyme has an optimal activity in the same pH range.
A method for enzyme-mediated dyeing of keratinous fibres, such as hair, has been described in WO 97/19999 (Novo Nordisk) and WO 97/19998 (Novo Nordisk).
Canadian patent 67:93913 discloses a composition containing a metal-containing dye for simultaneously permanent waving and dyeing hair. EP patent No. 328816 describes a process for dyeing of waved or relaxed hair using a metal ion-catalyzed hair dyeing composition.
There is still a need for a commercially viable method that allows (i.e., can be performed without significantly damaging the hair) simultaneous permanent setting (straightening or waving) and permanent dyeing of hair, with sufficient depth and permanence of color on hair.
A method that permits simultaneous permanent dyeing and setting of hair will give consumers a new range of options in their hair style choices. In particular, it will increase convenience for consumers, who will no longer have to wait weeks after a permanent setting treating prior to dyeing their hair.
The object of the present invention is to provide an improved method for permanent dyeing of chemically reduced hair such that the dyeing is suitably permanent, and sufficiently mild such that it does not cause significant damage to hair and can be performed immediately following, or, preferably, during a hair setting treatment. The present invention thus fulfills a long-standing industry need for a method that can provide permanent dyeing on chemically reduced hair without significant damage, thereby allowing a combined permanent setting and dyeing treatment.
It is advantageous to dye the reduced hair as an integrated component of a hair setting treatment not only to provide convenience for the customer, but also because the enzyme-mediated oxi- is dative process is an active and beneficial component in reformation of hair cross links, and dyeing of reduced hair is enhanced (both depth and permanence of color) relative to dyeing of hair in its normal, oxidized state.
The inclusion of small amounts of hydrogen peroxide or functional equivalents enhances dyeing of reduced hair relative to enzyme-mediated dyeing treatments not incorporating H2O2.
The present invention can be applied as part of a permanent hair waving or straightening process, preferably as part of a straightening process.
The present invention provides a method for treating reduced hair comprising contacting said hair with a composition comprising at least one oxidoreductase, at least one mediator, and at least one chemical oxidizing agent in an amount equivalent to 0.001-1% hydrogen peroxide calculated by weight of the composition.
It is also an object of the invention to provide a method for treating hair comprising
1) chemically reducing covalent disulfide linkages in the hair, and
2) contacting said hair with a composition comprising at least one oxidoreductase, at least one mediator, and at least one chemical oxidizing agent in an amount equivalent to 0.001-1% hydrogen peroxide calculated by weight of the composition.
Furthermore, it is an object of the invention to provide a method for treating hair comprising
1) chemically reducing covalent disulfide linkages in the hair,
2) mechanically straightening said hair, and
3) contacting said hair with a composition comprising at least one oxidoreductase, at least one mediator, and at least one chemical oxidizing agent in an amount equivalent to 0.001-1% hydrogen peroxide calculated by weight of the composition.
Example of chemical oxidizing agents are hydrogen peroxide, bromate, and other oxidants that generate hydrogen peroxide in situ such as percarbonates and perborates.
Cysteic acid quantification is frequently used to assess hair damage in oxidized hair. The cysteic acid assay described in the xe2x80x9cMaterials and Methodsxe2x80x9d section below is used to determine the extent of damage to hair. The hair is considered to be significantly damaged when the assayed value is higher than 1.00 mole-%. When the value is less than 1.00 mole-%, preferably less than 0.75 mole-%, the hair is not considered to be significantly damaged. Therefore, in the context of the present invention, a xe2x80x9cmild compositionxe2x80x9d is a composition that does not damage the hair significantly as defined above.
The term xe2x80x9creducedxe2x80x9d hair covers hair that has been subjected to a chemical reducing agent such that the amount of sulfhydryl groups in hair (primarily cysteine in its reduced, non-oxidized state) is at least three times higher than the normal level in comparable hair that has not been subjected to a reducing process. The amount of sulfhydryl groups in the hair can be s estimated using the thiol content assay described in the xe2x80x9cMaterials and Methodsxe2x80x9d section.
The term xe2x80x9cstraightenedxe2x80x9d hair covers hair that has been subjected to a chemical reduction treatment and has been mechanically oriented in a straight fashion, e.g., by combing. This definition covers both hair that has been subjected to a complete permanent hair straightening treatment, i.e., reduced and mechanically straightened hair that has been undergone oxidative fixation to reform cross links, and is therefore no longer in a reduced state, as well as hair that has only undergone a is partial or incomplete straightening treatment, i.e., hair that has been chemically reduced and mechanically straightened, but not subjected to an oxidative fixation (or may be in the middle of the slow process of air oxidation), and thus remains in a reduced state.
In general, the dyeing step is integrated into the hair straightening process by being applied within one day, preferably within one hour, even more preferably directly following removal (by rinsing) of the reducing agent.
In a preferred embodiment, the concentration of said chemical oxidant such as hydrogen peroxide is sufficient to enhance depth and permanence of color on hair, relative to systems containing only oxidoreductases, as well as to aid in reformation of hair cross links typically reduced in the first stage of a hair straightening process, but insufficient for permanent hair dyeing in the absence of oxidoreductase, and insufficient to cause significant damage to hair. According to the invention the chemical oxidizing agent is used in an amount equivalent to 0.001-1%, preferably 0.01-0.5%, calculated by weight of the dyeing formulation.